1. Technical Field
The present invention relates to a method of feeding a medium in a recording apparatus, which starts to feed a subsequent medium while recording is being performed on a previous medium being fed, and to a recording apparatus.
2. Related Art
A printer, which is a known example of recording apparatuses includes an auto sheet feeder (hereinafter, referred to as ASF) (for example, JP-A-2003-72964 or the like). When printing starts, the ASF is driven to feed an uppermost sheet from among sheets stacked in a cassette, and a leading end of the sheet is positioned at a printing start position.
The ASF starts to feed a subsequent sheet after a previous sheet has been printed and discharged. In the feeding method which starts to feed the subsequent sheet after the previous sheet has been printed, however, a relatively long standby time is present between the start of discharge of the previous sheet and the start of printing of the subsequent sheet. Accordingly, printing throughput is deteriorated.
In order to solve this problem, JP-A-2003-72964 discloses a recording apparatus that simultaneously performs a discharge operation of a previous sheet and a feeding operation of a subsequent sheet while maintaining a predetermined gap between the previous sheet and the subsequent sheet. That is, in the recording apparatus of JP-A-2003-72964, the position of a trailing end of the previous sheet is calculated on the basis of a transport distance of the previous sheet and sheet length data. Then, if two conditions that the trailing end of the previous sheet has passed through a specified position and a discharge command has been received are satisfied, the feeding operation of the subsequent sheet starts. According to this recording apparatus, the discharge operation of the previous sheet and the feeding operation of the subsequent sheet are simultaneously performed, while an inter-paper distance between the previous sheet and the subsequent sheet is ensured. Therefore, a standby time from the start of discharge of the previous sheet and the start of printing of the subsequent sheet can be shortened, and as a result printing throughput can be improved.
JP-A-2005-22792 (paragraphs [0029] to [0054]) discloses a sheet feeding device in which a leading end of a subsequent sheet is positioned in front of a feed/separation roller beforehand. In this case, before an instruction to control a feeding operation of the subsequent sheet is input, a pickup roller is driven to start a preliminary feeding operation. Then, if a pre-separation sensor detects a leading end of the subsequent sheet fed by the preliminary feeding operation, the pickup roller is stopped. In this sheet feeding device, if a post-separation sensor detects that the previous sheet has passed through the feed/separation roller, a control device starts to drive the pickup roller and the feed/separation roller.
JP-A-2001-278472 and JP-A-2002-145469 disclose a page printer in which, in order to improve throughput, a feeding operation of a next page starts before recording on a previous page is completed (so-called preceding feeding).
According to the recording apparatus of JP-A-2003-72964, if recording is performed to the end of the previous sheet (recordable last row), the discharge command is received a long time after transporting of the previous sheet was started. For this reason, a gap between the previous sheet and the subsequent sheet exists, and printing throughput is deteriorated.
In the recording apparatus of JP-A-2005-22792, after the subsequent sheet is preliminary fed, the feeding operation of the subsequent sheet starts when the post-separation sensor detects the passage of the previous sheet. The gap between the previous sheet and the subsequent sheet is defined by a gap between the pre-separation sensor and the post-separation sensor. The inter-sensor gap is not necessarily identical to a gap which should be ensured between the previous sheet and the subsequent sheet. For this reason, at some positions of the sensors in the recording apparatus, when the feeding operation of the subsequent sheet starts on the basis of the instruction to control the feeding operation, a sufficient gap between the previous sheet and the subsequent sheet may not be ensured. As described in the JP-A-2003-72964, an insufficient inter-paper gap results in a paper detection sensor not being able to detect the leading end of the subsequent sheet, and accordingly, it is difficult to manage the transport position of the subsequent sheet.
In such a case, in order to reliably ensure a sufficiently large gap, it is preferable to measure and confirm a gap between the previous sheet and the subsequent sheet after the preliminary feeding operation. If the subsequent sheet is positioned at a predetermined position after the preliminary feeding operation, the gap is relatively easily calculated. However, when the previous sheet and the subsequent sheet are double fed, the subsequent sheet may be double fed to a position beyond a target position of the preliminary feeding operation before the preliminary feeding operation is performed. In this case, it may be difficult to accurately calculate the gap between the previous sheet and the subsequent sheet.